Method of reducing the tendency of butadiene to polymerize



United States Patent US. Cl. 260-6665 Claims ABSTRACT OF THE DISCLOSURE Substituted aromatic nitro compounds of the general formulae:

wherein A is selected from the group consisting of 2N)n i C0NH NHCOCH and COC H n and m are each integer of 1-2; X is a halogen and R is hydrogen or an alkyl group of 1-4 carbon atoms at 0.0ll0% concentration in polar solvents such as dimethyl formamide, N-methyl pyrrolidone, acetonitrile etc. inhibit polymerization of butadiene.

This invention relates to a method of reducing the tendency of butadiene to polymerize in a polar solvent solution exposed to an elevated temperature.

It is known to use the techniques of solvent absorption and extractive distillation in processes for separating the valuable industrial raw material butadiene in good yield and high purity from a butadiene-containing hydrocarbon mixture such as the so-called C -hydrocarb0n fraction whose chief constituents are, for example, n-butane, isobutane, n-butenes, isobutene, butadiene, etc. It is also known that typical solvents used in these processes include dimethyl formamide, dimethylacetamide, N-methylpyrrolidone, acetonitrile and acetone.

In the operation of these processes, however, the solvent containing butadiene is necessarily exposed to elevated temperatures, e.g. from 80 to 160 C. or even higher, with the consequence that butadiene in the solvent tends to polymerize. As a result, an insoluble polymer is formed and difliculties arise from the clogging of the apparatus with the separating polymer and the formation of a polymeric coating on the inside wall of the apparatus, and so continuous operation over an extended period of time becomes practically diflicult.

At a room temperature or lower, the polymerization of butadiene may be prevented to some extent by addition of a conventionally known polymerization inhibitor, e.g. hydroquinone, 4-tert.-butyl-catechol, B-naphthylamine, Methylene Blue, sodium nitrite, etc. However, the polymerization inhibitors as named above are not satisfactory to prevent the polymerization of butadiene when the butadiene-containing solution is subjected to heat treatment at a relatively high temperature, say, 80160 C. or even higher over a long period of time.

An object of the present invention is to provide a method of preventing the polymerization of butadiene in a solution subjected to an elevated temperature and thereby to enable continuous operation of the solvent absorption or extractive distillation process for a long period of time. Other objects of the invention will be obvious from the contents of the specification hereinafter disclosed.

We have found that incorporation of at least one aromatic nitro compound of the below-mentioned general formula as the polymerization inhibitor or polymerization chain transfer agent (referred to hereinafter merely as polymerization inhibitor) into a butadiene-containing solution reduces tendency of butadiene to polymerize.

(OzN) 11 NH and H /N (OzN) n WI N (in which A is selected from the group consisting of CONH NHCOCHg and COC H n and m are each an integer of 1-2; X is a halogen and R is hydrogen or an alkyl group of 1-4 carbon atoms).

In particular, we have found that no or little polymerization of butadiene occurs even When the butadienecontaining solution incorporated with the above compound is subjected to an elevated temperature.

As the polymerization inhibitors for butadiene, nitrobenzene or its nuclear substitution derivative (substituent being alkyl, phenyl, nitro, halogen, etc.) has previously been proposed by the inventors but it has been found that the aromatic nitro compounds used in this invention are more effective than prior inhibitors.

According to this invention, the polymerization of butadiene can be prevented even in the presence of iron rust which rather promotes the polymerization of butadiene. Therefore, it is possible to carry out the extractive distillation and solvent absorption processes over an extended period of time Without employing apparatus made from such expensive materials as stainless steel. According to this invention, polymerization of butadiene is also prevented even when water is present in the butadienecontaining solution.

The polymerization inhibitors used in this invention may be applied to any solvent used in the separation of butadiene from hydrocarbon mixture containing butadiene by means of prior extractive distillation or solvent absorption process.

Although the amount of the polymerization inhibitor compound used is capable of wide variation depending upon such factors as the class of solvent, the water content of the solvent, operating conditions and the presence or absence of iron rust, in general, the objectives of this invention can be achieved by the incorporation of about 0.01l%, and preferably 0.05%, based on the weight of the solvent. Excess amount of the polymerization inhibitor causes no particular troubles.

Among the aromatic nitro compounds used in this invention are included monoand di-nitrobenzoic acid such as p-nitrobenzoic acid, 3,5-dinitrobenzoic acid;

alkyl nitrobenzoate such as ethyl p-nitrobenzoate;

nitrophthalic acid such as 3-nitrophthalic acid;

p-nitrophenylacetic acid and its alkyl ester;

nitrocinnamic acid and its alkyl ester such as p-nitrocinn'amic acid, ethyl o-nitrocinnamate;

monoand di-nitrophenol such as o-nitrophenol, 2,4-

dinitrophenol;

nitroresorcinol such as 4-nitroresorcinol;

monoand di-nitroalkylphenyl ether such as p-nitro phenetole, 2,4-dinitroanisole;

monoand di-nitroaniline such as p-nitroaniline, 2,4-dinitroaniline;

monoand di-nitro-N,N-dialkyl aniline such as N,N-dimethyl-p-nitroaniline, N,N-diethyl-2,4-dinitroaniline;

monoand di-nitrobenzoic acid halide such as p-nitrobenzoyl chloride, 3,5-dinitrobenzoyl chloride;

benzyl nitrohalide such as p-nitrobenzyl bromide;

nitrobenzyl alcohol such as p-nitrobenzyl alcohol;

benzyl nitrocyanide such as p-nitrocyanobenzyl;

nitrobenzylarnine such as p-nitrobenzylamine;

monoand di-nitrophenylhydrazine such as p-nitrophenylhydrazine, 2,4-dinitrophenylhydrazine;

monoand di-nitrobenzaldehyde such as m-nitrobenzaldehyde, 2,4dinitrobenzaldehyde; nitrophenyl isocyanate such as p-nitrophenyl isocyanate;

nitrobenzonitrile such as o-nitrobenzonitrile;

nitrobenzarnide such as m-nitrobenzamide;

monoand di-nitroacetanilide such as p-nitroacetanilide,

2,4-dinitroacetanilide;

nitrobenzophenone such as 4-nitrobenzophenone',

nitroanisidine such as S-nitro-o-anisidine;

monoand di-nitrosalicylic acid such as 3-nitrosalicylic acid or 3,5-dinitrosalicylic acid;

nitrophthalimide such as 4-nitrophthalimide;

nitrobenzimidazole such as S-nitrobenzimidazole.

Satisfactory polymerization inhibiting effect may be attained by single use of respective polymerization inhibitor for butadiene. Alternatively, the effect may be ensured by using such polymerization inhibitors in combination therewith or in combination with a polymerization inhibitor such as furfural, benzaldehyde, nitrobenzene, nitronaphthalene or its nuclear substitution derivative, a,fi-uinsaturated nitrile, aromatic merc-aptan, aliphatic nitro compound, cinnamic aldehyde, aldol, a-nitroso-fl-naphthol, isatin, morpholine, aliphatic tertiary mercaptan, alkyl nitrite, B,;3'-thiodipropionitrile or N- nitroso-N-methylaniline.

It has been found that the polymeriaztion inhibiting efiect of the aromatic nitro compounds used in this invention such as o-nitrophenol, 2,4-dinitrophenol, 2,4- dinitrophenylhydrazine and 4-nitrophthalimide is superior to that of nitrobenzene.

The effect of the polymerization inhibitor used in the invention is further promoted by the presence in the system of substances which are well-known as polymerization inhibitors or stabilizers for unsaturated compounds. Presumably, this is the result of a synergistic action between these substances and the additive used in accordance with the present invention. Known substances of this class include, for example, Methylene Blue, sodium nitrite, hydroquinone, sulphur, phenolic compounds such as 4-tert. butyl catechol, and aromatic amines such as fi-naphthylamine. The conventional amounts or less of such substances may be used.

The polymerization inhibitors according to this invention are also effective in the presence of saturated hydrocarbons such as butane or olefins such as n-butene and isobutene. Accordingly, when the present invention is applied to the separation of butadiene from C -hydrocarbon fraction by means of the prior solvent absorption or extractive distillation process, polymerization of butadiene is completely prevented and troubles on apparatus due to polymers separated out are entirely removed.

Further, the polymerization inhibitors according to this invention are not reduced at all in their etfect even in the presence of higher acetylenes such as methyl acetylene and vinyl acetylene. Accordingly, even in the presence of such higher acetylenes in the (l -hydrocarbon fraction, polymerization of butadiene is completely prevented and consequently butadiene may be separated in good yield.

Now the present invention will be explained in detail in conjunction with the followng examples.

EXAMPLE 1 A glass tube was charged with dimethyl formamide (DMF) and the polymerization inhibitor indicated in the table below. Butadiene was introduced under pressure to a gauge pressure of 5.5 kg./cm. while maintaining the temperature at 155 C. After 10 hours, state of the solution was examined and the following results were obtained.

Concentration (percent by Additive weight) State of the solution 1. None. Polymer separated out.

2. -N1trobenzo1c ac1d 0.5 Transparent.

3. thyl p-nitrobenzoate 0. 5 Practically transparent.

4. pNitr-ocinnarmc acid 0.5 Do.

5. Ethyl o-nitrocinnamate 0.5 Do.

6. o-Nitrophenol 0.5 Transparent.

7. 2,4-dinitrophenol 0.5 Do.

8. 4-nitr0resorcinol 0.5 Do.

0. 2,4-dinitroanil'm 0.5 Do.

10. N,N-d1ethyl-2,4-d 0.5 Practically transparent. 11. 3,5-dinitrobenzoylchlorlde 0.5 Do.

12. p-Nitrobenzyl cyanide 0.5 Transparent.

13. p-Nitrobenzylarnlne 0.5 Practically transparent. 14. p-Nltrophenylhydrazine t. 0.5 Transparent.

15. 2,4-d1n1trobeuzaldehyde 0.5 Practically transparent. 16. p-Nitrophenyl isocyanate 0. 5 D0.

17. o-Nitrobenzonitrile 0.5 Do.

18. rn-Nitrobenzarnide 0. 5 Slightly turbid.

10. 2,4-dinitroacetanilide. 0. 5 D0.

20. 4-nitrobenzophenone. 0.5 Transparent.

21. 4-nitrophthalimide 0. 5 D0.

EXAMPLE 2 EXAMPLE 4 A glass tube was charged with dimethyl formamide (DMF) and the polymerization inhibitor indicated in the An autoclave a yq a 9 q with DMF table below. Butadiene was introduced under pressure to and the Polymeflzatlon lnhlbltol md at d 1n the table a gauge pressure of 5.5 kg./cm. while maintaining the 5 below. Butadiene was mtroduced under pressure to a temperature at 155 C. After 24 hours, state of the solugauge pressure of 6 kg./cm. while maintaining the tion was examined and the following results were obtemperature at 155 C. After 48 hours, state of the solutained.

Concentration (percent by Additive weight) State of the solution 1. None Polymer separated out. 2. Sodium nitrate. 0.1 Turbid. 3. p-Nitrobenzoic acid- 0.5 Practically transparent. 4. o-Nitrophenol. 0.5 Transparent. 5. 2,4-dinitrophenol 0.5 Do. 6. 2,4-dinitroaniline... 0.5 Practically transparent. 7. p-Nitrophenylhydraz1ne 0.5 Do. 8. 2,4-dinitrophenylhydrazine 0.5 Transparent. 9. p-Nitrobenzylcyanide.-. 0.5 Do. 10. 4-nitrobenzophenone 0.5 Slightly turbid. 11. 4-nitrophthalimide 0.5 Practically transparent.

EXAMPLE 3 An autoclave having iron rust was charged with DMF tion was examined and the following results were 0band the polymerization inhibitor indicated in the table tained.

Concentrazign percen y Additive weight) State of the solution 1. None. Large amountt gt polymer se ara e out. 2. Sodium nitrite. 0. 1 Turbid. p 8. Sulfur 0. 1 Polygner crystallized ou 4. Methylene Blue 0. 1 Do. 2. i ti putycatechol. .d 0. 1 Do.

6632 ffi gf? }Practically transparent. 7. o-N1trophen0l 0i }TransparentI 1 0 Do. Methylene Blue 0.1 0. p-Nitrophenylhydrazine 1 D Sodium nitrite 0.1 i 11. 2, 4-dinitrophenyl-hydrazine- 1 D 4-t-butylcatechol 0.1 12. p-Nitrobenzyl cyanide 1 D Sodium nitrite 0.1 i 13. p-Nitroanisole 1 Sodium nitrite 0.1 i 14. 4-Nitrobenzophenone. 1 D

Methylene Blue 0. 1 i 15. 4-nitrophthalimide 1 D 4t-butylcatechol 0. 1 16. 5-nitrobenzimidazole 1 D Sodium nitrite 0.1

below. Butadiene was introduced under pressure to a EXAMPLE 5 gauge Pressure of 6 While maintaining the An autoclave having iron rust was charged with DMF, temperature at 155 C. After 48 hours, state of the solu- 60 by weight of Sodium nitrite and 1% by weight of tion was exam n and the fOHOWII-Ig results were the polymerization inhibitor indicated in the table below. tamed. Butadiene was introduced under pressure to a gauge pressure of 6 kg./cm. while maintaining the temperature at 155 C. After 24 hours, state of the solution was examined and the following results were obtained.

EXAMPLE 6 Eflect obtainable by joint use of two kinds of the polymerization inhibitors was examined by the same way as carried out in the Example 3. The polymerization inhibitors were each added in 0.5% by weight.

Additive State of the solution 1) o-Nitrophenol Transparent.

2,4-dinitrophenylhydrazine (2) o-Nitrophenol Do.

4-nitrophthalimide (3) 2,4-dinitroaniline Practically 4-nitrophthalimide transparent. (4) 2,4-dinitrophenylhydrazine Transparent.

4-nitrophthalimide (5) o-Nitrophenol Do.

2,4-dinitrophenol (6) 2,4-dinitroaniline Practically 2,4-dinitrophenol transparent.

EXAMPLE 7 An autoclave having iron rust was charged with N- methylpyrrolidone and the polymerization inhibitor as indicated 'below. Butadiene was introduced under pressure to a gauge pressure of 5.5 kg./cm. while maintaining the temperature at 120 C. After 48 hours, state of the solution was examined and the following results were 8 EXAMPLE 8 An autoclave having iron rust was charged with acetonitrile and the polymerization inhibitor as indicated below. Butadiene was introduced under pressure to a gauge pressure of 13 kg./cm. while maintaining the temperature at 120 C. After 24 hours, state of the resulting solution was examined and the following results were obtained.

Concentration (percent by Additive Weight) State of the solution 1. N itrobenzene 0. 1 Slightly turbid. 2. o-NitrophenoL. 0. l Practically transparent. 3. 2,4-dinitropheno 0.1 Transparent. 4. 2,4-dinitroaniline 0.1 Slightly turbid. 5. p-Nitrobenzyl cyanide... 0. 1 Practically transparent. 6. 2,4 dinitrophenylhydrazine 0. 1 Transparent. 7. 4-nitrophthalimide 0 1 Do.

What we claim is:

1. A method of reducing the tendency of butadien to polymerize in a polar solvent solution exposed to an elevated temperature, which comprises adding to the solution, at least one aromatic nitro compound of the formulae A is selected from the group consisting of COOR, CH COOR, -CH=CHCOOR, OR, NR COX, CH X, CH OH, CH CN, CH NH NHNH CHO, NCO, CN, CONH NHCOCH and COC H n and m are each an integer of 1-2; X is a halogen and R is hydrogen or an alkyl group of 1-4 carbon atoms.

2. A method according to claim 1, wherein said butadiene comprises a C -hydrocarbon fraction.

3. A method according to claim 1, wherein said soluobtamed. tion comprises a polar solvent selected from the group Concentratign (percent y Additive Weight) State of the solution 1. None Large amount of polymer separated out. 2. Sodium nitrite 0. 1 Polymer crystallized out. 3. Sulfur 0.1 Do. 4. Methylene Blue. 0. 1 Do. 5. 4-t-butylcatecho 0.1 Do. g. tzJ-gllifiropherlioln 1 'lragsparent.

. 'ni rop ieno 1 )0. 8. 2,4-dinitroanilin 1 Practically transparent. 9. 2,4-dinltrophenylhydrazine. 1 Transparent. 10. 44113;;goplhthalilngide. (i 1 Practically transparent. 11. piro enzy romi e sodium nitrite 1 Transparent. 12. p-Nitrobenzophenone 1 D0.

Methylene Blue 0. 1 13. o-Nitropheno1 1 D0.

4-t-butylcatechol. 0. l 14. 2,4-dinitrophenol l Do Sulfur 0.1 15 2,4-dinlt10am l 1 Do.

Sodium nitrite. 0.1 1 16. 2,4-dinitrophenylhydrazinu. l t Du.

4-t-butylcatechol 0.1 i 17. 4-nitr0phthalmiide l l Do.

Methylene Blue 0.1 l

solution.

5. A method according to claim 4, wherein the amount is 0.05 to 5%.

References Cited UNITED STATES PATENTS Craig 2039 Boyer et a1 203-9X Drake et al 203-9X Coover et a1. 260-4659 Buehler 2039 10 2,888,386 5/1959 Brower 203-92X 3,309,412 3/1967 Sakuragi et a1 260-6665 3,340,160 9/1969 Waldby 252405X 3,405,189 10/1968 Sakuragi et a1 260-6665 3,407,240 10/ 1968 Sakashita et al 260-6665 FOREIGN PATENTS 20,281 8/1968 Japan 260-6665 DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant Examiner 

